A phrase coined by comedian Johnny Sanchez, relating to an older man of Mexican heritage who, during the process of aging, developed a stomach so large his arms seems to shrink in comparison, making him akin to a tyrannosaurus rex.

The term came to fruition through Sanchez noticing how as Mexican men age, they tend to morph into the description of Tyrannosaurus Mex with larger stomachs and seemingly smaller arms.

Johnny - Look at that guy! Look at that gut!
Bobby - Yeah! And his tiny arms! He's totally a tyrannosaurus mex.